Matrix multiplication

In a stationery shop, a pen costs \.20, a notebook costs \$2.50 and a file costs \$3.40.
In another shop, a pen costs \$0.30 less, a notebook costs \$0.60 more and a file costs \$0.80 less than in the first shop.

The prices can be represented by the matrix
$Q = \begin{bmatrix}1.20 & 2.50 & 3.40\\0.90 & 3.10 & 2.60\end{bmatrix}.$

A customer buys 3 pens, 2 notebooks and 1 file from each shop.

Find the total amount he spends in the second shop by evaluating a suitable matrix product.